The present invention relates generally to lures for attracting and controlling Diabrotica species. In particular, the invention relates to lures comprising one or more compounds found in the volatile fraction of Cucurbita blossoms, or analogs thereof, alone or in combination with other lures, insecticides, and/or compulsive feeding stimulants.
The chrysomelid genera Diabrotica and Acalymma contain numerous pest species, including the western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte; the southern corn rootworm (SCR) or, the spotted cucumber beetle, D. undecimpunctata howardi [D. duodecimpunctata Fab.]; the northern corn rootworm (NCR), D. barberi Smith and Lawrence; and the striped cucumber beetle (SCB), Acalymma vittatum (Fabr.).
The western, northern, and southern corn rootworms are the most expensive insect pests of North America and annually cost U.S. farmers approximately one billion dollars in yield loss and in cost of preventative treatments with soil insecticides. The era of relatively cheap crop protection against these pests has ended because of generalized rootworm resistance to organochlorine insecticides and the withdrawal of registrations for these insecticides by the U.S. EPA due to widespread environmental contamination. The newer organophosphorous and carbamate insecticides are more expensive and subject to accelerated microbial degradation in soils and a rapid loss of activity. Furthermore, due to the persistence of many of these soil insecticides, groundwater and surface run-off pollution is of much concern to state and federal agencies. Because of the uncertain performance and safety of the major products currently used for larval grootworm control, such as carbofuran (Furadan.TM.), isofenphos (Amaze .TM.), phorate (Thimet.TM.), terbufos (Counter.TM.), a technological void exists for controlling these pests. Even standard cultural methods of pest management such as crop rotations of corn-soybean-corn and corn are endangered as evidence exists that the northern corn rootworm can undergo an extended diapause for two seasons. Hence, the benefits of yearly crop rotation are threatened.
Present soil insecticide technology for corn rootworm control is rapidly becoming unworkable. The use of volatile attractants, singularly and in combinations with other control methods, can become the basis for a new integrated pest management (IPM) technology for rootworm control that is economically favorable for the farmer and certainly much less environmentally objectionable. In this regard, Diabrotica and Acalymma are known to show a close association with host plants of the family Cucurbitaceae, particularly with the genus Cucurbita. Adult beetles are most commonly found in the blossoms of Cucurbita species where they feed on pollen (in staminate flowers) and on nectar. In most instances, adult beetles showed a preference for the blossoms of C. maxima Duchesne cultivars over those of C. pepo L. and C. moschata Poir.
The blossom characteristics, i.e., color, size, shape, and/or fragrance, responsible for this preference are not fully understood, although Diabrotica attraction to certain compounds, termed semiochemicals, has been reported. By way of background, semiochemicals are plant-produced compounds which act by diffusion through air to produce behavorial responses in associated insect species. Kairomones are those semiochemicals which act to benefit the receiving species; allomones are those which benefit the sending species; and synomones, e.g., floral volatiles involved in pollination, benefit both the emitting plant, through pollination, and the perceiving insect by rewards of nectar and pollen or through more intangible ecological rewards of aggregation or lek formations which lead to mating.
One of the earlier reports relating to Diabrotica attraction to compounds appeared in Morgan, et al., J. Econ. Entomol., 21:913 (1928). This collection of preliminary results on the chemotropic response of certain insects included the observation that the spotted cucumber beetle, D. undecimpunctata howardi (as D. duodecimpuntata Fab.), was attracted to cinnamaldehyde and cinnamyl alcohol. These results were obtained using white granite-ware pans of about 2-quart capacity set in rows on stakes 2 feet high, and filled with 1 quart of water to which was added 1 cc. of the chemical to be tested. The areas in which experiments were conducted included a field white with the blossoms of the field daisy (Erigeron annuus) oatfields, margins of woods, hedge rose, a cane brake, a slaughter-house lot, and a livery-stable yard. There is no indication in the reference as to the degree to which, or the conditions under which, cinnamic aldehyde and cinnamic alcohol acted as attractants. Snapp, et al., J. Econ. Entomol., 22:98 (1929) disclosed a preliminary report indicating that the spotted cucumber beetle was attracted by oil of thyme (white) and benzyl alcohol. However, in tests by Lampman, et al, J. Chem. Ecol., 13:959 (1987) benzyl alcohol was shown to have negligible attractant value.
Ladd, et al., J. Econ. Entomol., 76:1049 (1983), studying a mixture of phenethyl proprionate, eugenol, geraniol, a food-type lure for Japanese beetles, reported that eugenol was attractive to adults of D. barberi Smith & Lawrence (NCR), but not attractive to D. virgifera virgifera LeConte (WCR). Ladd, T. L., J. Econ. Entomol., 77:339 (1984) tested nine compounds closely related to eugenol for attractancy to NCR including four groups: eugenol and its close relatives with isomeric or saturated hydrocarbon side chains; eugenol acetate and its isomer; anethole an its analogs with isomeric or saturated side chains; and a miscellaneous group consisting of methyleugenol and 2-allyl-6-methoxyphenol (orthoeugenol). The author reported two new attractants for NCR, isoeugenol and 2-methoxy-4-propylphenol and concluded that while neither the position of the double bond in the side chain nor the degree of saturation was critical in attracting the NCR, the presence of the methoxy and hydroxyl groups at their respective positions, particularly the latter, seemed to be important. Yaro, et al., Environ. Entomol., 16:126 (1987) reported that eugenol and 2-methoxy-4-propyl phenol were highly attractive to D. cristata Harris (a non-pest species) and D. barberi Smith & Lawrence, whereas isoeugenol acetate was not attractive. None of the compounds was highly attractive to D. virgifera vigifera LeConte. Ladd, et al., J. Econ. Entomol., 77:652 (1984) also conducted tests to study the influence of color and height of eugenol-baited sticky traps and reported that the traps were most effective when painted yellow and placed 0 to 0.25 m above ground.
Another recent report of investigations concerning a chemical basis for Diabrotica orientation to the blossoms or foilage of Cucurbita species was in Andersen, et al., J. Chem. Ecol., 12:687 (1986). The authors screened C. maxima "Blue Hubbard" blossom volatiles for electroantennogram (EAG) activity, a laboratory test for insect electrophysiological response to volatile compounds, and found two fractions had significant activity for the southern corn rootworm. The first peak consisted of indole and the second, smaller peak, was not characterized. Indole was then field tested for insect responsiveness and found to be a potent attractant of the western corn rootworm and of the striped cucumber beetle. However, the southern corn rootworm was not attracted at any dosage level despite the strong EAG response.
Andersen, et al., J. Chem. Ecol., 13:681 (1987) subsequently characterized the blossom constituents of attractive Cucurbita floral volatiles from a number of cultivars representing C. moschata, C. pepo, and C. maxima, and examined other factors, including nutritional and secondary chemical characteristics, that might influence beetle field distribution in blossoms. They found paradimethoxybenzene to be a major constituent of headspace samples from cultivated Cucurbita cultivars. The Diabrotica species showed a clear preference for certain cultivars. SCR preferred the blossoms of C. maxima cultivars, while WCR preferred the cultivars of C. maxima as well as a single cultivar of C. pepo. The authors suggested that NCR and SCR are similar in their host preferences, each strongly favoring C. maxima, whereas WCR appeared to find a broader range of cultivars acceptable. No firm conclusions were reached with respect to whether the gustatory cues, i.e., the levels of cucurbitacins, and olfactory cues, i.e., floral odors and level of release, acted individually or in concert, along with visual qualities to produce the patterns of preferences exhibited by the various species of Diabrotica.
Seasonal variations in responses to attractants have also been observed. As noted earlier, Andersen, et al., J. Chem. Ecol., 12:687 (1986) found that indole elicited a strong EAG response from SCR, but was wholly ineffective as an attractant in field tests. However, Lampman, et al., J. Chem. Ecol., 13:959 (1987) subsequently found that indole was in fact a moderately active attractant for SCR late in the season. In that study, the authors field tested various blossom volatiles and related compounds and found that southern, western, and northern corn rootworm adults exhibited not only a species specific response but also a seasonal pattern of response to sticky traps baited with various benzenoid compounds. SCR adults were attracted in early to mid-August to traps baited with veratrole (1,2-dimethoxybenzene), phenylacetaldehyde, and chavicol (4-hydroxy-1-allylbenzene). In late August and September, SCR trap catches dramatically increased for veratrole and phenylacetaldehyde, as well as for some compounds previously unattractive compounds, such as indole, several eugenol-related compounds, benzyl acetone, and phenethyl alcohol. WCR adults were significantly attracted to a different group of compounds, namely estragole, trans-anethole, and indole. Estragole (4-methoxy-1-allylbenzene) was an effective WCR attractant from early August until the end of the trapping period in late September and early October. Indole and trans-anethole (4-methoxy-1-propenylbenzene) were less effective attractants than estragole and were most active at the beginning and/or end of the corn season. The paramethoxy ring substituent and the position of the double bond in the propanoid side chain were noted to be critical for maximum WCR response; compounds differing in either aspect were less attractive. The phenyl propanoids, eugenol and isoeugenol, significantly attracted NCR adults. Ladd, T. L., J. Econ. Entomol., 77:339 (1984) previously found that NCR response is optimal for phenylpropanoids with a metamethoxy and parahydroxy substituent. Both Ladd, supra, and Lampman, et al., supra, noted a seasonal variability in response to eugenol and isoeugenol.
A comparison between the rootworm species indicated that the ecologically similar NCR and WCR adults are attracted to structurally related phenylpropanoids and both species respond to changes in the ring substituents of the major attractants. However. WCR and NCR adults are not attracted to the same phenylpropanoids, although SCR adults are to eugenol and isoeugenol (NCR attractants). The authors in Lampman, et al., supra also noted (and subsequently reported in Metcalf, et al., J. Econ. Entomol., 80:870 (1987)) an increase in SCR trap catch for either eugenol or veratrole added to insecticide-impregnated cucurbitacin baits. Apparently, SCR adults cross-responded (especially late in the season) to some WCR and NCR attractants, although the main attractants for each species was highly specific.
The foregoing results suggested that Diabrotica are attracted to certain single component attractants; however, none of these attractants demonstrated the requisite degree of attraction required to effectively control and manage populations of Diabrotica. Thus, there exits a need in the art for an alternative safe and effective method for management of Diabrotica species which is effective in controlling the more visible stage of the insect pests, i.e., the adult, yet which is economical and which abolishes the need for the use of soil insecticides.